CVE-2024-46744

In the Linux kernel, the following vulnerability has been resolved:

Squashfs: sanity check symbolic link size

Syzkiller reports a "KMSAN: uninit-value in pick_link" bug.

This is caused by an uninitialised page, which is ultimately caused

by a corrupted symbolic link size read from disk.

The reason why the corrupted symlink size causes an uninitialised

page is due to the following sequence of events:

1. squashfs_read_inode() is called to read the symbolic

link from disk. This assigns the corrupted value

3875536935 to inode->i_size.

2. Later squashfs_symlink_read_folio() is called, which assigns

this corrupted value to the length variable, which being a

signed int, overflows producing a negative number.

3. The following loop that fills in the page contents checks that

the copied bytes is less than length, which being negative means

the loop is skipped, producing an uninitialised page.

This patch adds a sanity check which checks that the symbolic

link size is not larger than expected.

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V2: fix spelling mistake.